Answer:
The manager will put 6 parakeets each in 7 cages and 6 canaries each in 3 cages.
Explanation:
We will find the greatest common factor of 42 and 18 to know the answer.
42 = 2 x 3 x 7
18 = 2 x 3 x 3
So, greatest common factor is

So, 42 parakeets need
cages
And 18 canaries need
cages
So, the manager will put 6 parakeets each in 7 cages and 6 canaries each in 3 cages.